Well, shrug it off. Routine nags about sourpussies fill up our complaint corner, if that can make you feel better, and we have so many foul customer service threads here about this, but honestly, just ignore it and enjoy the books. There are some nice folks here, too, you just have to run into them, I bet there are some at the library too. Be consistently nice, the sourpussies might melt, it takes effort to be mean, so they are bound to get tired. If not, wear a badge that says
I love library girls, I just bought one in Prague.
By the way, nobody will rent you anything without you registering on your valid ID, so that's not a CH myth, only.